HIGH Cr Ni-BASED ALLOY WELDING WIRE, SHIELDED METAL ARC WELDING ROD, AND WELD METAL FORMED BY SHIELDED METAL ARC WELDING

ABSTRACT

Provided is a high Cr Ni-based alloy welding wire with which tensile strength and weld cracking resistance of a welded portion, the integrity of the microstructure of a welded metal, and inhibition of scale generation are improved. The high Cr Ni-based alloy welding wire is configured to have an alloy composition comprising, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si: 0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0 to 31.5%, Ta: 1 to 10%, and Mo: 1 to 6%, and as inevitable impurities, Ca+Mg: less than 0.002%, N: 0.1% or less, P: 0.02% or less, O: 0.01% or less, S: 0.0015% or less, H: 0.0015% or less, Cu: 0.08% or less, and Co: 0.05% or less, and the balance: Ni. Then, the high CrNi-based alloy welding wire is configured such that the contents of S, Ta, Al, and Ti satisfy the following relation (1) and the contents of Ta, Mo, and N satisfy the following relation (2): 
       12000S+0.58Ta−2.6Al−2Ti£19.3  (1)
 
       Ta+1.6Mo+187N 3 5.7  (2).

TECHNICAL FIELD

The present invention relates to a high Cr Ni-based alloy welding wire,a shielded metal arc welding rod, and a weld metal formed by shieldedmetal arc welding that are used for welding in a pressurized waterreactor type nuclear power plant or the like which operates at a hightemperature.

BACKGROUND ART

A high Cr Ni-based alloy welding material disclosed in each of thefollowing Patent Documents 1 to 9 and the following Non-Patent Document1 has been known, as a high Cr Ni-based alloy welding material to beused for a member of a steam generator in a pressurized water reactortype nuclear power plant that operates at a high temperature of 300 to350° C., or the like.

Patent Documents 1 and 2 each discloses a technology for improving ahigh temperature strength characteristic by adding N.

Patent Document 3 discloses a technology for reducing hot cracking, coldcracking, root cracking, and stress corrosion cracking and alsoobtaining desired strength and desired corrosion resistance by reducingcontents of Al and Ti and addition of Nb.

Patent Document 4 discloses a technology for reducing scale on a weldbead surface and increasing weld cracking resistance by reducingcontents of Al and Ti and adding Ta in place of Nb.

Patent Document 5 discloses a technology for reducing various types ofcracking including ductility-dip cracking when build-up welding isperformed on a SUS304 steel plate, by addition of Mo and Nb+Ta.

Patent Document 6 discloses a technology for reducing stress corrosioncracking, solidification cracking, ductility-dip cracking, and rootcracking and obtaining desired strength by addition of Mo and Nb+Ta, andfurther addition of a trace of Ca+Mg.

Patent Document 7 discloses a technology for eliminating the need for astabilization process by addition of Nb, and preventing reduction ofcorrosion resistance and reduction of weldability due to S, by additionof Mn.

Patent Document 8 discloses a technology for obtaining an alloyexcellent in metal dusting resistance by addition of Cu, Nb, Ta, Mo, andthe like to a high Cr Ni-based alloy.

Patent Document 9 discloses a technology for improving weld crackingresistance and hot workability of the wire by addition of Nb and Mn andadjustment of the content of Nb+Mn.

Non-Patent Document 1 discloses a technology about ductility-dipcracking generated in a Ni-based alloy welded metal (Ni-based alloy 82and Ni-based alloy 52). Non-Patent Document 2 discloses the chemicalcomposition of a high Ni-based alloy welding material specified by eachof the standard by the American Welding Society (AWS) and the standardby the American National Standard Institute (ANSI).

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP 3170166-   Patent Document 2: JP 3170165-   Patent Document 3: JP 2003-501557A-   Patent Document 4: WO 2005/070612-   Patent Document 5: US 2004/0115086A1-   Patent Document 6: WO 2008/021650A2-   Patent Document 7: JP 06-89426A-   Patent Document 8: JP 2004-197150A-   Patent Document 9: JP 2009-22989A-   Non-Patent Document 1: M. G. COLLINS, A. J. RAMIREZ, AND J. C.    LIPPOLD Welding Journal, December 2003. 348S˜-   Non-Patent Document 2: American Welding Society “Specification for    Nickel and Nickel-Alloy Bare Welding Electrodes and Rods” AWS    A5.14/A5.14M: 2009 An American National Standard Institute.

OVERVIEW OF THE INVENTION Technical Problem

In a welded metal portion of a welded portion in a device that operatesat a high temperature of 300 to 350° C., high temperature strengthcomparable to that of a base material is demanded. In a conventionalwelded joint of Ni-based alloy 690, high temperature strength of awelded metal may be reduced than that of a base material. Consequently,it has become a challenge to develop a welding material that exhibitshigher reliability in terms of stabilization of high temperaturestrength. In the technology disclosed in each of Patent Documents 1 and2 described above, high temperature strength is improved bystrengthening a solid solution using N. However, solubility of N in theNi-based alloy is extremely low. Thus, addition of N beyond the limit ofthe solubility may cause generation of a pore in the welded metal.Further, this technology may promote deposition of a nitride such as Ti,N, and may also cause reduction of ductility of the welded metal. Thus,there is a limit to improvement in the strength by addition of N.

The technology disclosed in Patent Document 3 is the one for improvingthe stress corrosion cracking and weld cracking susceptibility byaddition of Nb. The technology disclosed in Patent Document 6 is the onefor improving the stress corrosion cracking and weld crackingsusceptibility by addition of Mo and Nb Ta. Though each of PatentDocuments 3 and 6 describes about the strength, the strength is notspecifically disclosed in its embodiment example.

The inventions of Patent Documents 4, 5, 7, 8, and 9 do not discloseabout strength at all. The structure of the high Cr Ni-based alloy is acomplete austenite structure of low solubility with respect to animpurity element such as P or S, and is used for welding of a thickstructural member with a high reaction stress in an actual device. Thus,excellent weld cracking resistance is demanded for this type of weldingmaterial. In the high Cr Ni-based alloy, S, which has an extremely lowsolubility in the austenite structure, very markedly affects weldcracking susceptibility. The reaction stress of a welding wire includinga conventional level of S increases when performing welding of the thickstructural member. Thus, a micro-crack is generated in a welded portionwhen a bend test is conducted.

In the technology of each of Patent Documents 1 to 9, an upper limit ofthe content of S is set in order to obtain the weld cracking resistance.However, it is not adequate to set the upper limit in view of thewelding work of the thick structural member. On the other hand, thecontent of Mn that tends to combine with S may be increased in shieldedmetal arc welding, according to the Boiler and Pressure Vessel Code ofthe American Society of Mechanical Engineers (ASME). Thus, S may befixed as MnS having a high melting point, and an adverse effect on aweld cracking due to grain boundary segregation of S may be therebyreduced. Accordingly, a limiting value for the content of S shieldedmetal arc welding may be relaxed more than that in a TIG welding wire.In the austenite structure, H has a high solubility, and has a smalldiffusion rate. Thus, there is no concern about delayed cracking or thelike of the welded metal of a ferrite-based structure due to diffusivehydrogen. However, hydrogen embrittlement cannot be ignored in a portionof the Ni-based alloy where stress corrosion cracking or ductility-dipcracking poses a problem. Accordingly, hydrogen embrittlement resistanceis also demanded. His mixed into the wire due to attachment of alubricant to a surface of the wire or the like when the wire is meltedor drawn. In the shielded metal arc welding, H is mixed into the wirefrom a flux as well. Detailed observation of the microstructure of thewelded metal has shown that, when the content of H exceeds a certainvalue, a microvoid is generated at a grain boundary as an initial stateof stress corrosion cracking or ductility-dip cracking. With the high CrNi-based alloy filler material disclosed in Patent Document 4, there isa limit to reducing scale on the weld bead surface to be generatedduring TIG welding. A portion of a welding material (composition rangeof elements of ERNiCrFe-13) standardized by the AWS in Non-PatentDocument 2 is shown in Table 1. In actual production of the weldingmaterial, optimization of contents of elements such as Nb, Ta, Mo, Al,Ti, Mg, Ca and allowances for contents of inevitable impurities to bemixed into the welding material when the wire is drawn or produced bymelting should be adequately studied. Otherwise, practical applicationof the welding material is impossible.

TABLE 1 AWS Standards for Ni-Based Alloy Welding Wire (Mass %) StandardsC Mn Fe P S Si Cu Ni AWS A5.14 0.03 1.0 Rem. 0.02 0.015 0.50 0.3052.0-62.0 ERNiCrFe-13 or less or less or less or less or less or less AlTi Cr Nb + Ta Mo Co B Zr 0.50 0.50 28.5-31.0 2.1-4.0 3.0-5.0 0.10 0.0030.02 or less or less or less or less or less

In view of the actual situation described above, an object of thepresent invention is to provide a high Cr Ni-based alloy welding wirewith which tensile strength and weld cracking resistance of a weldedportion, the integrity of the microstructure of a welded metal, andwelding performance are improved.

Another object of the present invention is to provide a high Cr Ni-basedalloy shielded metal arc welding rod and a weld metal formed by shieldedmetal arc welding, which achieve improvement in tensile strength andweld cracking resistance of a welded portion and improvement in theintegrity of the microstructure of a welded metal.

Solution to Problem

A high Cr Ni-based alloy welding wire of the present inventioncomprises, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si:0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0 to 31.5%,Ta: 1 to 10%, Mo: 1 to 6%, and N: 0.1% or less, and as inevitableimpurities, P: 0.02% or less, O: 0.01% or less, S: 0.0015% or less, H:0.0015% or less, Cu: 0.08% or less, and Co: 0.05% or less, and thebalance: Ni.

In the present invention, the contents of S, Ta, Al, Ti, Mo, and Nsatisfy the following relations (1) and (2):

12000S+0.58Ta−2.6Al−2Ti≦19.3  (1)

Ta+1.6Mo+187N≧5.7  (2).

Inventors of the present invention have studied a condition of the highCr Ni-based alloy welding wire for improving tensile strength and weldcracking resistance of a welded portion, the integrity of themicrostructure of a welded metal, and welding performance. The weldedmetal is a metal of the welded portion where the welding wire and a basematerial are melted. As a result of the study, the inventors have founda relationship between improvement in the weld cracking resistance andthe contents of S, Ta, Al and Ti is established by the above relation(1) and a relationship between improvement in the tensile strength ofthe welded portion and the contents of Ta, Mo, and N is established bythe above relation (2), in addition to the above-mentioned chemicalcomposition of Ta and the like. By configuring the welding wire to havethe above-mentioned chemical composition and to satisfy theabove-mentioned relations (1) and (2), there may be provided the high CrNi-based alloy welding wire which achieves excellent tensile strengthand excellent weld cracking resistance of the welded portion andimprovement in the integrity of the microstructure of the welded metaland improvement in welding performance. The calculated value of theabove relation (1) is set to 19.3 or less. The smaller the calculatedvalue of the above relation (1) is, the more the weld crackingresistance tends to increase. For that reason, the calculated value ofthe above relation (1) may be set to be 13 or less in order to obtainremarkable weld cracking resistance.

The inventors have found that, in a conventional high Cr Ni-based alloywelding wire mainly comprising Nb and Ta as group V elements, Taimproves performance such as strength, without reducing weld crackingresistance, while presence of Nb added in order to improve the weldcracking resistance remarkably reduces the weld cracking resistance. Nb(niobium) is an element for generating a compound with carbon andnitrogen and then increasing corrosion resistance. An effect ofincreasing strength may also be obtained from the use of Nb, due todeposition strengthening and solid solution strengthening. The study ofthe inventors, however, has revealed that, although weld crackingsusceptibility during build-up welding on a SUS 304 plate tends toincrease as the content of Nb increases, the weld crackingsusceptibility does not tend to increase but slightly decrease as thecontent of Ta increases. Then, by adopting the chemical compositionincluding only Ta (not including Nb) as the group V element as in thepresent invention, a high Cr Ni-based welding wire that achievesexcellent weld cracking resistance in particular may be provided.

A description will be given below about an effect expected for eachelement included in the high Cr Ni-based alloy welding wire of thepresent invention and the reason for limiting the content of eachelement.

C (carbon) is an element for strengthening a solid solution. With anincrease in the content of C, the tensile strength increases. However,when the content of C exceeds 0.04 mass %, stress corrosion crackingresistance decreases. The content of C is therefore set to 0.04 mass %or less in view of these respects. Preferably, the lower limit of thecontent of C is set to 0.006 mass % in order to obtain the effect ofincreasing the tensile strength. It is assumed in this application that0 mass % is not included in the mass % or less.

Mn (manganese) exerts deoxidation and desulfurization actions duringwelding. Mn fixes harmful S which may cause a weld hot cracking therebyreducing weld cracking susceptibility. However, when the welding wireincludes Mn whose content exceeds 7 mass %, slag fluidity is reducedduring the welding, resulting in reduced welding performance. Thus, thecontent of Mn is set to 7 mass % or less. The content of Mn in a weldingwire is prescribed to be 1.0 mass % or less in the Boiler and PressureVessel Code of the ASME. However, preferably, the lower limit of thecontent of Mn is set to 0.05 mass % in order to obtain the effect ofreducing a weld hot cracking.

Fe (iron) is effective for stabilizing a metal structure at hightemperature, and reduces aging embrittlement. Thus, it is necessary toinclude content of Fe of 1% or more. However, when the content of Feexceeds 12 mass %, ductility-dip cracking occurs due to grain boundarycarbide deposition, thereby reducing the corrosion resistance and thestress corrosion cracking resistance. Accordingly, the content of Fe isset to 1 to 12 mass %.

Though Si (silicon) exerts a deoxidation effect and increases thefluidity during the welding, weld hot cracking susceptibility increaseswhen the content of Si increases. Thus, the content of Si is set to 0.75mass % or less. Preferably, the lower limit of the content of Si is setto 0.05 mass % in order for Si to exert the deoxidation effect and toincrease the fluidity.

Al (aluminum) is mainly used as a deoxidation agent when a welding wirerod is produced by melting. Al has an effect of reducing the weldcracking susceptibility. Further, Al fixes N in a weld metal, thuscontributing to improvement in the strength, as an N-stabilizingelement. The weld metal is a metal of a welded portion in which awelding rod is molten and from which slag is removed. It is necessary toinclude the content of Al of 0.01 mass % or more in order for Altoexhibit these effects. However, when the content of Al is excessive,slag floats on the surface of a molten pool during TIG welding or MIGwelding. This slag adheres firmly to the surface of the welded metal asa scale film, and an incomplete fusion or the like may be thereforecaused. The welding performance may be thereby reduced. Accordingly, theupper limit of the content of Al is set to 0.7 mass %. When the contentof Al is in the range of 0.26 mass % or more, the tensile strength andthe weld cracking susceptibility of the welded portion and the weldingperformance may be clearly improved with a good balance. Accordingly,the lower limit of the content of Al may be set to 0.26 mass % (or thecontent of Al may be set to 0.26 to 0.7 mass %), in view of balanceamong the tensile strength and the weld cracking susceptibility of thewelded portion and the welding performance. Preferably, the content ofAl is low in order to obtain stable and excellent welding performancewith no production of the scale film even under a high heat input suchas during plasma TIG welding. However, preferably, the content of Al isset to 0.05 to 0.5 mass % in order to reduce the weld crackingsusceptibility as well as to obtain the stable and excellent weldingperformance.

Ti (titanium) is used as a deoxidation agent, and has an effect ofreducing the weld cracking susceptibility, like Al. Ti also contributesto improving hot workability during production of a filler material.Further, Ti has a strong affinity for N, and deposits as TiN. Due tothis property, a fine structure of the welded portion may be obtained,thus contributing to improvement in the tensile strength. It isnecessary to include the content of Ti of 0.01 mass or more in order forTi to exert these effects. However, when the content of Ti is excessive,slag is produced during the welding, and the welding performance isthereby reduced, as in the case of Al. Thus, the content of Ti is set to0.01 to 0.7 mass %. When the content of Ti is in the range of 0.36 mass% or more, the tensile strength and the weld cracking susceptibility ofthe welded portion and the welding performance may be clearly improvedwith a good balance. Accordingly, as in the case of Al, the lower limitof the content of Ti may be set to 0.36 mass % (or the content of Ti maybe set to 0.36 to 0.7 mass %), in view of balance among the tensilestrength and the weld cracking susceptibility of the welded portion andthe welding performance. Preferably, the content of Ti is set to 0.05 to0.5 mass % in order to improve the welding performance and to reduce theweld cracking susceptibility, as in the case of Al.

Cr (chromium) is an element essential for enhancing the corrosionresistance. It is necessary to include the content of Cr of 25.0 mass %or more in order for Cr to exert a satisfactory effect for the stresscorrosion cracking resistance. However, when the content of Cr exceeds31.5 mass %, the hot workability during production of the fillermaterial is remarkably reduced or the ductility-dip cracking due to thegrain boundary carbide deposition is promoted. Thus, the content of Cris set to 25.0 to 31.5 mass %.

Ta (tantalum) is a congener of Nb. Ta generates a compound with carbonand nitrogen and increases the corrosion resistance, which is similar toNb. However, Ta is different from Nb in that even if the content of Tais increased, the number of cracks in the weld cracking does notincrease during the build-up welding on the SUS 304 plate. Thus, even ifTa is the congener of Nb, the behavior of the weld cracking cannot beadjusted by the content of Nb+Ta. Addition of Ta increases the strengthcaused by the deposition strengthening and the solid solutionstrengthening. The effect of addition of Ta is manifested when thecontent of Ta is 1 mass % or more. However, when the content of Ta thatexceeds 10 mass % is included, the tensile strength will excessivelyincrease and ductility will decrease. Thus, the content of Ta is set to1 to 10 mass %.

Mo (Molybdenum) is an element for effectively increasing the strength bythe solid solution strengthening. The effect of Mo is manifested whenthe content of Mo is 1 mass % or more. However, when the content of Mothat exceeds 6 mass % is included, the tensile strength will excessivelyincrease and the ductility will decrease. Thus, the content of Mo is setto 1 to 6 mass %.

P (phosphorus) is an inevitable impurity that produces eutectic with Ni(Ni—Ni₃P or the like) having a low melting point. When the content of Pis large, the weld cracking susceptibility is increased. Thus, thesmaller content of P is better. However, excessive limitation of P leadsto lowered economical efficiency. Thus, the content of P is set to 0.02mass % or less.

O (oxygen) is an inevitable impurity that comes from the atmosphereduring production of the filler material by melting. O gathers at thegrain boundary of the welded metal in the form of an oxide and thenreduces high temperature strength of the grain boundary. Further, Oincreases the weld cracking susceptibility. Thus, the content of O isset to 0.01 mass % or less.

N (nitrogen) is an inevitable impurity, like O. It is thereforeimportant to set the limit value for the content of N. N combines withTi or the like to form a nitride (TiN or the like), and contributes toincreasing the tensile strength. However, when the content of N exceeds0.1 mass high temperature ductility decreases. Thus, the content of N isset to 0.1 mass % or less.

S (sulfur) is an inevitable impurity that that produces eutectic with Nihaving a low melting point, like P. S is an element that is extremelylow in solubility with respect to a Ni-based alloy, tends to segregateat the grain boundary, and promotes the weld cracking susceptibilitymost. Assume that a welded joint of a thick structural member having ahigh reaction stress is fabricated and then a bend test is conducted onthe welded portion. A weld cracking transitionally expands when thecontent of S exceeds 0.0015 mass %. Thus, the content of S is set to0.0015 mass % or less.

H (hydrogen) is an inevitable impurity to be mixed into the wire due toattachment of a lubricant when the wire is melted or drawn. H is trappedat a location with a high residual stress or by a carbide, which maycause occurrence of a microvoid due to hydrogen embrittlement. Theintegrity of the microstructure may be thereby reduced. Accordingly, thecontent of H is set to 0.0015 mass % or less.

Cu (copper) is an inevitable impurity whose dilution ratio is large whenbuild-up welding is performed on a carbon steel plate. Cu increases theweld cracking susceptibility when a considerable amount of Fe isincluded in the welded metal. Cracking that may be generated due to anincrease in the content of Cu is generated because, Fe, which has beenmixed into the welded metal from the carbon steel during the build-upwelding on the carbon steel plate, does not dissolve into Cu at all.This cracking is generated due to an increase in the content of S asdescribed above. This cracking and a weld cracking at the welding jointof the thick structural member are different in terms of a welding workcondition and a cause of generation. Cu is, however, included as animpurity element in the melting material. Thus, in view of this respect,the content of Cu is set to 0.08 mass % or less.

Co (cobalt) is an inevitable impurity having a long half life. When suchCo is included for a pressurized water reactor, radioactivated Cocirculates together with an oxide and the like in a nuclear reactorsystem when Ni-based alloy 690 is used, and then increases aradioactivity level when a periodic inspection or the like is made.Thus, it is better not to include Co in the welding wire. However, about1 or 2% of Co is originally included in the Ni-based material. Thus, inview of this respect, the content of Co is set to 0.05 mass % or less.

When Ca (calcium) and Mg (magnesium) are further included as inevitableimpurities, preferably, the total content of Ca and Mg is controlled tobe less than 0.002 mass %. Each of Ca and Mg is an element having astrong affinity for O or S, exerts strong deoxidation anddesulfurization effects, and may reduce the weld crackingsusceptibility. Ca and Mg promote scale generation on a weld beadsurface more notably than Al and Ti. Thus, Ca and Mg are treated as theinevitable impurities. Especially when the total content of Ca and Mg is0.002 mass % or more, scale generation tends to notably occur.Accordingly, preferably the total content of Ca and Mg is controlled tobe less than 0.002 mass % or less.

As described above, the chemical composition including Ta alone as thegroup V element is preferable in view of only the drawback of Nb ofreducing the weld cracking resistance. However, Nb is the element thatis effective for improving the corrosion resistance and the strength,like Ta. In addition, Nb is lower in cost than Ta. Then, a part of Tamay be substituted for by Nb, in view of these advantages. In this case,the content of Nb is set to 0.5 mass % or less, and the elementsincluded in the welding wire are so adjusted that the contents of S, Ta,Nb, Al, Ti, Ta, Mo, and N satisfy the following relations (3) and (4):

12000S+0.58Ta+2.1Nb−2.6Al−2Ti≦19.3  (3)

Ta+3.8Nb+1.6Mo+187N≧5.7  (4).

The inventors have studied a condition of a high Cr Ni-based alloywelding wire for improving tensile strength and weld cracking resistanceof a welded portion, the integrity of the microstructure of a weldedmetal, and a scaling inhibition effect, even when Nb is added. As aresult, the inventors have found that a relationship between improvementin the weld cracking resistance and the contents of S, Ta, Nb, Al and Tiis established by the above relation (3) and a relationship betweenimprovement in the tensile strength of the welded portion and thecontents of Ta, Nb, Mo, and N is established by the above relation (4),in addition to the above-mentioned chemical composition of Nb and thelike. By configuring the welding wire to have the above-mentionedchemical composition of Ta, Nb, and the like and to satisfy theabove-mentioned relations (3) and (4), the high Cr Ni-based alloywelding wire that achieves excellent tensile strength and excellent weldcracking resistance of the welded portion, excellent integrity of themicrostructure of the welded metal, and excellent welding performancemay be provided. In addition, the manufacturing cost of the welding wiremay be reduced. The calculated value of the above relation (3) is alsoset to be 19.3 or less, like that in the above relation (1). The smallerthe calculated value of the above relation (3) is, the more the weldcracking resistance tends to increase. For that reason, the computedvalue of the above relation (3) may also be set to be 13 or less.

Preferably, the high Cr Ni-based alloy welding wire of the presentinvention further comprises, by mass, at least one kind of elementselected from B (boron), Zr (zirconium), and rare earth elements (REM):0.02% or less. B in a Ni-based alloy deposits along the grain boundarymore preferentially than a sulfide that embrittles the grain boundary athigh temperature. Thus, B has an effect of strengthening the grainboundary. B is especially effective for reducing ductility-dip crackingat high temperature. Preferably, B in the range of 0.001 to 0.005 mass %is added.

Zr has a strong affinity for O, and therefore has a function as adeoxidation agent. However, when an adding amount of Zr is large, Zrproduces an eutectic compound with Ni having a low melting point. Theweld cracking susceptibility is thereby increased.

As the rare earth elements, La (lanthanum), Ce (cerium), and the likeare used. The rare earth element has large deoxidation anddesulfurization effects, and has an effect of reducing a cracking thatmay be generated during hot processing due to strengthening of the grainboundary and an effect of reducing the weld cracking susceptibility.When the adding amount of the rare earth element is large, however, aneutectic compound with Ni having a low melting point is produced. Theweld cracking susceptibility is thereby increased.

Each of B, Zr, and the rare earth elements has an effect of increasingthe weld cracking resistance. However, the same effect may be obtainedby combined addition of B, Zr, and the rare earth elements. Excessiveaddition of B, Zr, and the rare earth elements, however, increases theweld cracking susceptibility. Accordingly, the high Cr Ni-based alloywelding wire of the present invention comprises 0.02 mass % or less ofat least one kind of element selected from B, Zr, and the rare earthelements.

When the high Cr Ni-based alloy welding wire of the present invention isbased on ERNiCrFe-13 of AWS A5.14/A5.14M: 2009, the alloy composition ofthe high Cr Ni-based alloy welding wire should satisfy the compositionrequirements of the invention, and then may comprise by mass, C: 0.03%or less, Mn: 1.0% or less, Si: 0.50% or less, Fe: 1 to 12%, Al: 0.5% orless, Ti: 0.5% or less, Cr: 28 to 31.5%, Nb: 0.5% or less, Nb Ta: 2.1 to4.0%, Mo: 3.0 to 5.0%, B: 0.003% or less, and Zr: 0.02% or less, and asinevitable impurities, Ca+Mg: less than 0.002%, Cu: 0.08% or less, Co:0.05% or less, P: 0.02% or less, S: 0.0015% or less, O: 0.01% or less,N: 0.1% or less, H: 0.0015% or less, and the balance: Ni.

In this case, preferably, the content of Ni is set to 52.0 to 62.0 mass%.

A high Cr Ni-based alloy welding wire of the present invention may beused in the form of a shielded metal arc welding rod. In this case, thechemical composition of the shielded metal arc welding rod comprises, bymass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si: 0.75% or less,Al: 0.26 to 1.0%, Ti: 0.36 to 1.0%, Cr: 25.0 to 31.5%, Nb: 3.0% or less,Ta: 3.0% or less, and Mo: 1 to 6%, and as inevitable impurities, N: 0.1%or less, and, P: 0.02% or less, S: 0.0015% or less, O: 0.01% or less, H:0.0015% or less, Cu: 0.08% or less, and Co: 0.05% or less, and thebalance: Ni.

An effect expected for each element included in the shielded metal arcwelding rod of the present invention and the reason for limiting thecontent of each element are almost the same as those in the case of theabove-mentioned high Cr Ni-based alloy welding wire. The reason forlimiting the content of Al in the shielded metal arc welding rod of thepresent invention to 0.26 to 1.0 mass % is to ensure improvement intensile strength and weld cracking susceptibility of a welded portion,and ensure improvement in welding performance. The reason for limitingthe content of Ti to 0.36 to 1.0 mass % is to ensure improvement in thetensile strength and the weld cracking susceptibility of the weldedportion and ensure improvement in the welding performance. That is, noscale is generated on the weld bead surface of the shielded metal arcwelding rod, unlike in the case of TIG welding or the like. Thus, thelower limits of the contents of Al and Ti of the welding wire may berespectively increased to 0.26 mass % and 0.36 mass %. With thisarrangement, deoxidation and desulfurization effects may be increasedduring welding, the weld cracking susceptibility may be reduced, and thetensile strength may be improved. When the contents of Al and Ti eachexceed 1.0 mass %, however, slag detachability is reduced and thewelding performance is therefore reduced. Thus, the upper limits of thecontents of Al and Ti are each set to 1.0 mass %.

The reason for limiting the content of Nb to 3.0 mass % or less is tomaintain excellent welding performance and excellent weld crackingresistance, and to improve tensile strength while reducing manufacturingcost as described above, even if a part of Ta is substituted for by Nb.On the other hand, when Nb is added from the welding wire (core wire forthe shielded metal arc welding rod) and when the content of Nb exceeds3.0 mass %, slag burns and the welding performance is thereby reduced.Thus, the upper limit of the content of Nb is set to 3.0 mass %.

The reason for limiting the content of Ta to 3.0 mass % or less is toimprove the tensile strength of the welded portion while maintaining theexcellent welding performance and the excellent weld cracking resistanceby including Ta. On the other hand, when Ta is added from the weldingwire (core wire for the shielded metal arc welding rod) and when thecontent of Ta exceeds 3.0 mass %, slag burns and the welding performanceis therefore reduced. Thus, the upper limit of the content of Ta is setto 3.0 mass %. When the high Cr Ni-based alloy welding wire of thepresent invention is used for the shielded metal arc welding rod asdescribed above, the tensile strength and the weld cracking resistanceof the welded portion, the integrity of the microstructure of a weldedmetal, and the welding performance may be increased.

When the high Cr Ni-based alloy welding wire of the present invention isused for the shielded metal arc welding rod, a weld metal after thewelding comprises the following alloy composition. That is, there may beobtained the weld metal formed by the shielded metal arc weldingcomprising, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si:0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0 to 31.5%, NbTa: 1.8 to 4.5%, Mo: 1 to 6%, and as inevitable impurities, the totalcontent of Ca and Mg: less than 0.002%, N: 0.1% or less, P: 0.02% orless, S: 0.005% or less, O: 0.1% or less, H: 0.002% or less, Cu: 0.08%or less, and Co: 0.05% or less, and the balance: Ni.

An effect of each element included in the weld metal formed by theshielded metal arc welding according to the present invention and thereason for limiting the content of each element are almost the same asthose in the case of the above-mentioned high Cr Ni-based alloy weldingwire. The reason for limiting the content of S to 0.005 mass % or lessin the weld metal formed by shielded metal arc welding rod according tothe present invention is that a trace of S is included in a fluxcovering the welding rod, thereby increasing the content of S in theweld metal. However, according to the Boiler and Pressure Vessel Code ofthe ASME, the content of Mn in a shielded metal arc welding rod may beincreased to fix S as MnS with a high melting point, and an adverseeffect on a weld cracking due to grain boundary segregation of S may bethereby reduced. No scale attaches to the weld bead surface of theshielded metal arc welding rod, unlike in case of the TIC welding or thelike. Thus, the contents of Al and Ti in the wire may be increased. Withthat arrangement, deoxidation and desulfurization effects may beincreased and weld cracking susceptibility may be thereby reduced duringwelding. In view of these respects, the content of S in the weld metalformed by the shielded arc welding rod of the present invention isrelaxed more than the limiting value for the welding wire.

The weld cracking susceptibility may be reduced for the reason describedabove. Thus, the content of Nb may be increased more than in the case ofthe welding wire. Nb is the element that is effective for improving thecorrosion resistance and the strength, like Ta, and is lower in costthan Ta, as described above. Thus, by replacing apart of Ta with Nb,manufacturing cost may also be reduced. Then, in the weld metal formedby the shielded metal arc welding rod of the present invention, thecontent of Nb+Ta in the welded metal is set to 1.8 to 4.5 mass %. Whenthe content of Nb+Ta exceeds 4.5 mass %, weld cracking resistance may bereduced, or slag may burn on the weld bead surface, thereby reducingwelding performance. Nb and Ta may be added from the flux as alloyelements. In addition, when added from the welding wire to be used forthe shielded metal arc welding rod, Nb and Ta may be more stablytransferred to the welded metal.

During shielded metal arc welding, an oxide-based slag obtained bymelting of a flux remains in a weld metal as a non-metal inclusion.Thus, the weld metal includes a larger content of O that formed by theTIG welding. Then, the content of O as the inevitable impurity in theweld metal formed by the shielded metal arc welding according to thepresent invention is set to 0.1 mass %. Preferably, the content of H isset to 0.002 mass % or less. The reason for limiting this content of His that moisture absorbed by the flux newly generates hydrogen, and thecontent of H is therefore relaxed from the limiting value for H in thecase of the welding wire, in view of this respect.

When the welding elements are added from the welding wire, the weldingwire having the content of Nb of 3.0 mass % or less may be used.However, when the content of Nb in the wire exceeds 3.0 mass %, slagburns on the weld bead surface. Then, the upper limit of the content ofNb is set to 3.0 mass %. Further, when each of the contents of Al and Tiin the welding wire exceeds 1.0 mass %, slug detachability is reduced,and the welding performance is therefore reduced. Thus, the upper limitsof the contents of Al and Ti are each set to 1.0 mass %.

Preferably, the content of at least one kind of element selected from B,Zr, and rare earth elements in the shielded metal arc welding rod andthe weld metal formed by the shielded metal arc welding according to thepresent invention is set to 0.02% or less. The effect and the reason forlimiting the content of each element are the same as those in the caseof the high Cr Ni-based alloy welding wire described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A includes photographs each showing a result of a dye penetranttest conducted on a build-up welded portion formed on a SUS 304 plate byTIG welding using an embodiment (Example 2) of the present invention.

FIG. 1B includes photographs each showing a result of the dye penetranttest conducted in a similar manner using a comparative example(Comparative Example 12) of the present invention.

FIG. 1C is a photograph enlarging a portion of FIG. 1B (portionindicated by an arrow).

FIG. 1D is a sectional view showing the groove surface of the SUS 304plate used in FIGS. 1A and 1B.

FIG. 2A is a plan view of a welded joint for a restraint weld crackingtest of a thick plate (thick structural member) for evaluating weldcracking resistance.

FIG. 2B is a front view of FIG. 2A.

FIG. 3A is a graph showing a relationship between the content of Nb anda result of the dye penetrant test of a build-up welded portion on theSUS 304 plate formed by the TIG welding.

FIG. 3B is a graph showing a relationship between the content of Ta andthe result of the dye penetrant test.

FIG. 4 is a graph showing a relationship between the content of S in awelding wire and a result of a side bend test conducted on a portion ofthe thick plate (thick structural member) restraint-welded by the TIGwelding.

FIG. 5A is a structure photograph of a section of a welded metal formedby using the embodiment (Example 1) of the present invention taken by anoptical microscope at a magnification of approximately 200.

FIG. 5B is a structure photograph of a section of a welded metal formedby using a comparative example (Comparative Example 8) to the presentinvention taken by the optical microscope under the condition same as5A.

FIG. 6A is a photograph of a weld bead surface of Comparative Example 12of the present invention taken by a scanning electron microscope (SEM)at a magnification of approximately 400.

FIG. 6B is a graph showing a result of qualitative analysis of the weldbead surface using a scanning electron microscope-energy dispersiveX-ray analysis (SEM-EDX).

MODE FOR CARRYING OUT THE INVENTION

An embodiment of a high Cr Ni-based alloy welding wire of the presentinvention will be described below. Table 2 shows alloy compositions ofhigh Cr Ni-based alloy welding wires in the embodiment of the presentinvention and alloy compositions of Comparative Examples for confirmingan effect of the present invention.

TABLE 2 Chemical Compositions of Welding Wires (Mass %) Wire C Mn Fe P SSi Cu Ni Al Ti Cr Nb Ta Symbol (%) (%) (%) (ppm) (ppm) (%) (%) (%) (%)(%) (%) (%) (%) Example 1 Y1 0.023 1.26 10.2 60 6 0.25 0.03 Rem. 0.120.25 27.8 — 1.1 Example 2 Y2 0.022 0.45 8.5 20 7 0.71 0.005 Rem. 0.150.25 25.5 0.15 2.2 Example 3 Y3 0.021 3.28 9.2 10 5 0.86 0.003 Rem. 0.310.36 28.9 0.23 1.2 Example 4 Y4 0.02 0.15 9.5 100 5 0.26 0.05 Rem. 0.320.36 29.6 — 1.05 Example 5 Y5 0.016 0.09 7.1 50 6 0.21 0.04 Rem. 0.170.22 30.0 — 2.5 Example 6 Y6 0.016 0.35 6.56 110 4 0.32 0.02 Rem. 0.320.41 29.5 0.01 2.3 Example 7 Y7 0.031 6.68 3.5 50 6 0.51 0.06 Rem. 0.210.32 30.1 — 5.8 Example 8 Y8 0.025 0.69 3.2 20 8 0.46 0.01 Rem. 0.290.20 25.2 — 6.2 Example 9 Y9 0.015 2.51 1.2 60 4 0.21 0.005 Rem. 0.160.42 26.2 — 9.2 Example 10 Y10 0.021 0.45 8.4 30 8 0.15 0.02 Rem. 0.260.37 29.5 0.41 2.2 Example 11 Y11 0.032 0.38 8.4 40 4 0.26 0.01 Rem.0.28 0.40 29.8 0.32 3.0 Example 12 Y12 0.015 0.74 9.2 20 5 0.25 0.02Rem. 0.09 0.12 29.2 — 1.3 Example 13 Y13 0.022 0.9 9.8 50 10 0.26 0.03Rem. 0.41 0.49 30.2 0.09 1.15 Example 14 Y14 0.029 1.1 6.5 60 10 0.320.02 Rem. 0.56 0.64 30.6 0.07 2.8 Example 15 Y15 0.016 1.2 7.4 80 120.28 0.01 Rem. 0.68 0.65 29.1 0.01 2.2 Example 16 Y16 0.035 0.75 2.4 407 0.52 0.07 Rem. 0.16 0.23 31.2 — 5.7 Comparative Y17 0.009 0.03 9.32 3010 0.11 0.12 Rem. 0.32 0.41 30.6 — — Example 1 Comparative Y18 0.01 0.360.01 80 8 0.07 0.01 Rem. 0.22 0.31 28.71 0.10 10.5 Example 2 ComparativeY19 0.021 0.45 9.9 100 15 0.36 0.05 Rem. 0.15 0.25 29.3 0.83 0.01Example 3 Comparative Y20 0.03 0.36 11.5 80 6 0.25 0.03 Rem. 0.007 0.00830.1 0.03 1.2 Example 4 Comparative Y21 0.025 0.48 6.3 50 5 0.42 0.04Rem. 0.71 0.73 29.3 — 3.3 Example 5 Comparative Y22 0.023 0.9 6.22 40 200.09 0.06 Rem. 0.11 0.24 30.06 0.10 2.3 Example 6 Comparative Y23 0.0110.26 8.2 80 17 0.12 0.01 Rem. 0.63 0.51 28.9 0.03 3.7 Example 7Comparative Y24 0.026 0.24 11 30 20 0.18 0.06 Rem. 0.70 0.52 28.96 —0.01 Example 8 Comparative Y25 0.006 0.81 11.8 100 10 0.03 0.08 Rem.0.078 0.18 29.33 — 0.97 Example 9 Comparative Y26 0.007 0.81 10.5 50 100.02 0.09 Rem. 0.081 0.18 28.93 — 1.2 Example 10 Comparative Y27 0.020.26 10 50 5 0.26 0.04 Rem. 0.07 0.21 23.8 — 0.78 Example 11 ComparativeY28 0.02 0.31 8.79 40 5 0.11 0.05 Rem. 0.13 0.18 29.5 2.51 0.01 Example12 Mo Co O N H Ca + Mg B Zr REM Relations (%) (%) (ppm) (%) (ppm) (ppm)(ppm) (ppm) (ppm) (1) (3) (2) (4) Example 1 1.2 0.03 45 0.016 8 — — — —7.0 — 6.0 — Example 2 3.2 0.01 30 0.02 7 17 — — — — 9.1 — 11.6 Example 31.3 0.04 15 0.021 7 — 10 — — — 5.7 — 8.1 Example 4 1.5 0.02 20 0.02 9 1020 15 30 5.1 — 7.2 — Example 5 5.0 0.04 30 0.015 9 — 10 — 50 7.8 — 13.3— Example 6 4.2 0.03 50 0.005 13 — 10 50 60 4.5 — 10.0 — Example 7 3.20.01 20 0.015 12 — 60 — — 9.4 — 13.7 — Example 8 2.5 0.02 30 0.012 11 —— — — 12.0 — 12.4 — Example 9 1.6 0.03 25 0.028 8 10 — — — 8.9 — 17.0 —Example 10 2.1 0.01 90 0.016 10 19 — — — — 7.9 — 10.5 Example 11 3.20.02 70 0.026 7 17 — — — — 5.7 — 14.2 Example 12 1.5 0.005 40 0.03 5 18— — — 6.3 — 9.3 — Example 13 2.4 0.03 20 0.025 7 — — — — — 10.8 — 10.0Example 14 3.4 0.005 25 0.008 11 — — — — — 11.0 — 10.0 Example 15 3.40.03 15 0.033 7 — — — — 12.6 — 13.8 — Example 16 4.5 0.04 15 0.025 7 — —— — 10.6 — 17.6 — Comparative — 0.05 10 0.023 10 10 — — — 10.3 — 4.3 —Example 1 Comparative 10.5 0.03 69 0.009 8 — — — — — 14.7 — 29.4 Example2 Comparative 0.02 0.03 50 0.01 10 — — — — — 18.9 — 5.1 Example 3Comparative 1.3 0.01 60 0.03 9 — — — — — 7.9 — 9.0 Example 4 Comparative3.1 0.02 40 0.03 7 — — — — 4.6 — 13.9 — Example 5 Comparative 3.1 0.0631 0.01 10 11 — — — — 24.8 — 9.5 Example 6 Comparative 3.4 0.01 20 0.00910 15 — — — — 20.0 — 10.9 Example 7 Comparative 0.01 0.03 55 0.008 25 16— — — 21.1 — 1.5 — Example 8 Comparative 0.02 0.02 30 0.007 10 30 10 — —12.0 — 2.3 — Example 9 Comparative 0.02 0.04 45 0.02 25 25 20 20 10 12.1— 5.0 — Example 10 Comparative 0.02 0.02 22 0.011 7 — — — — 5.9 — 2.9 —Example 11 Comparative 3.51 0.01 28 0.006 7 90 — 20 — — 10.6 — 16.3Example 12 Relations: (1) 12000S + 0.58Ta − 2.6Al − 2Ti ≦ 19.3 (2) Ta +1.6Mo + 187N ≧ 5.7 (3) 12000S + 0.58Ta + 2.1Nb − 2.6Al − 2Ti ≦ 19.3 (4)Ta + 3.8Nb + 1.6Mo + 187N ≧ 5.7

Examples 1 to 16 in Table 2 show the alloy compositions of the weldingwires in this embodiment. The welding wire in each of Example 1 to 16comprises, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si:0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0 to 31.5%,Ta: 1 to 10%, and Mo: 1 to 6%, and as inevitable impurities, P: 0.02% orless, O: 0.01% or less, N: 0.1% or less, S: 0.0015% or less, H: 0.0015%or less, Cu: 0.08% or less, and Co: 0.05% or less, and the balance: Ni.The contents of S, Ta, Al, Ti, Mo, and N in each of Examples 1, 5, 6, 7,8, 9, 12, 15, and 16 satisfy the following relations (1) and (2):

12000S+0.58Ta−2.6Al−2Ti≦19.3  (1)

Ta+1.6Mo+187N≧5.7  (2).

Further, the content of Nb in each of Examples 2, 3, 4, 10, 11, 13, and14 satisfies a condition of 0.5 mass % or less, and the contents of S,Ta, Nb, Al, Ti, Ta, Mo, and N in each of Examples 2, 3, 4, 10, 11, 13,and 14 satisfy the following relations (3) and (4).

12000S+0.58Ta+2.1Nb−2.6Al−2Ti≦19.3  (3)

Ta+3.8Nb+1.6Mo+187N≧5.7  (4).

Further, the content of Al in each of Examples 3, 4, 6, 8, 10, 11, 13,14, and 15 satisfies a condition of 0.26 to 0.7 mass %. The content ofTi in each of Examples 3, 4, 6, 9, 10, 11, 13, 14, and 15 satisfies acondition of 0.36 to 0.7 mass %.

The content of Nb in each of Examples 2, 4, 9, 10, 11, and 12 satisfiesthe condition of 0.5 mass % or less, and the total content of Ca and Mgas an inevitable impurity satisfies a condition of less than 0.002 mass%.

The content of at least one kind of element selected from B, Zr, andrare earth elements in each of Examples 3 to 7 further satisfies acondition of 0.02 mass % or less.

Table 3 shows evaluation results obtained by conducting a tensile teston a weld metal, a dye penetrant test on a build-up welded portion, aside bend test on a welded metal portion of a thick structural member, acheck test of a microstructure (presence or absence of a microvoid inthe structure of a welded metal) in the section of the welded metal, anda test for checking presence or absence of scale generation on thebuild-up surface (weld bead surface) of multiple layers on a carbonsteel plate resulting from build-up welding. The weld metal is formed byusing each of the high Cr Ni-based alloy welding wires of the variousalloy compositions shown in Table 2.

TABLE 3 Evaluation of Welding Wire Characteristics Tensile StrengthResult of Side Bend Test (MPa) on Welded Portion of Thick Presence orTest Temperature Result of Structural Member Presence of Absence ofScale (° C.) Penetration Test Total Absence of Generation on Room onBuild-Up Cracking No. of Microvoid in Welded Welded Metal Temp. 350Portion Length (mm) Defects Pass/Fail* Metal Structure Structure Example1 634 501 No Indication of 1.2 3 Pass None None Defect Example 2 712 551No Indication of 3.3 5 Pass None None Defect Example 3 702 505 NoIndication of 0.5 1 Pass None None Defect Example 4 645 515 NoIndication of 0 0 Pass None None Defect Example 5 720 558 No Indicationof 0 0 Pass None None Defect Example 6 719 555 No indication of 0 0 PassNone None Defect Example 7 734 564 No indication of 1.8 2 Pass None NoneDefect Example 8 752 575 No Indication of 3.1 7 Pass None None DefectExample 9 760 578 No Indication of 4.4 7 Pass None None Defect Example10 707 552 No Indication of 4.0 5 Pass None None Defect Example 11 724557 No Indication of 1.4 3 Pass None None Defect Example 12 660 525 NoIndication of 0 0 Pass None None Defect Example 13 677 524 No Indicationof 4.4 7 Pass None None Defect Example 14 720 556 No indication of 4.0 6Pass None None Defect Example 15 705 553 No indication of 5.5 8 PassNone None Defect Example 16 751 572 No Indication of 4.6 6 Pass NoneNone Defect Comparative 570 460 Indication of 7.7 11 Fail None NoneExample 1 Defect Comparative 810 576 No Indication of 12.5 14 Fail NoneNone Example 2 Defect Comparative 572 460 Indication of 13.0 13 FailNone None Example 3 Defect Comparative 660 510 No Indication of 7.5 11Fail None None Example 4 Defect Comparative 722 562 No indication of 0 0Pass None Present Example 5 Defect Comparative 705 553 Indication of22.1 25 Fail None None Example 6 Defect Comparative 725 562 Indicationof 17.5 20 Fail None None Example 7 Defect Comparative 571 444Indication of 23.1 16 Fail Present None Example 8 Defect Comparative 620470 No Indication of 4.9 6 Pass None Present Example 9 DefectComparative 623 482 Indication of 6.5 9 Pass Present Present Example 10Defect Comparative 580 446 No Indication of 0.5 1 Pass None None Example11 Defect Comparative 727 575 Indication of 5.2 9 Pass None PresentExample 12 Defect *Notes (Ministerial Ordinance No. 81): (1) A crackshould not exceed 3 mm in length (except those occurring at edge cornersof a test (2) The total length of cracks having a length of 3 mm or lessshould not exceed 7 mm. (3) The number of cracks and/or blowholes shouldnot exceed 10.

In the tensile test, tensile strengths of the weld metal at roomtemperature and at 350° C. were measured, based on JIS G 0202. When thetensile strength measured at the room temperature is included in a rangeof 610 to 780 MPa and the tensile strength measured at 350° C. isincluded in a range of 485 MPa or more, the measured tensile strengthresulting from the tensile test was evaluated to be good. The reason whythe appropriate ranges of the tensile strength are set to such numericalvalue ranges is as follows. When the tensile strength is less than 610MPa at the room temperature or less than 485 MPa at 350° C., asatisfactory strength characteristic of the weld metal cannot obtained.When the tensile strength exceeds 780 MPa at the room temperature,reduction of ductility or an excessive increase in the residual stressof the welded portion may be caused.

Evaluation of high-temperature cracking susceptibility using the dyepenetrant test was conducted at the build-up welded portion of thegroove surface of a SUS 304 thick-walled plate, as a preparatory stepfor production of a welded joint of a thick structure member for arestraint weld cracking test shown in FIGS. 2A and 2B that will bedescribed later. In the dye penetrant test, build-up welding of three tosix layers was performed on the groove surface with a groove width ofapproximately 60 mm and a groove length of approximately 250 mm by TIGwelding (see FIGS. 1A to 1D). Then, a process surface obtained bydeleting an excess metal portion was formed by machining to achieve apredetermined groove shape. The dye penetrant test was conducted on thisprocess surface, based on JIS Z 2343-1, and then presence or absence ofa weld cracking was visually checked (see FIGS. 1A to 1C).

The side bend test was conducted, based on JIS Z 3122. A bend test pieceof a shape with a plate thickness of 10 mm was taken from the weldedjoint of the thick structure member, and a guided bend test method usingjigs of a male type and a female type was carried out on the bent testpiece. The male type jig was pressed against the female type jig so thatthe test piece is bent to form a U-character shape. The curvature radius(R) of the surface of the test piece in that case was set to twice theplate thickness, or R was set to be equal to 20 mm. After the test, thebent surface was observed by a magnifying glass, and the number ofcracks (or blowholes) produced at the welded portion and the length ofthe cracks were measured. Based on the ministerial ordinance (No. 81)defining technical standards for welding of an electrical work piece,evaluation of the side bend test was made according to the followingrequirements (1), (2), and (3):

(1) The length of a crack (except the one that occurs at an edge cornerof the bend test piece) should not exceed 3 mm.(2) The total length of cracks that satisfy the above requirement (1)should not exceed 7 mm.(3) The number of cracks and/or blowholes should not exceed 10 pieces.The bend test piece that has satisfied all of the above requirements (1)(2) and (3) was evaluated to have passed the side bend test. The bendtest piece that does not satisfy one of the above requirements (1) to(3) was evaluated not to have passed the side bend test.

In the check test of the microstructure, the section of the welded metalof the thick structural member (SS 400) shown in FIGS. 2A and 2B wasmagnified to about 15 to 400 times its original size, using an opticalmicroscope to check presence or absence of a microvoid. As a test pieceof observation by the optical microscope, the test piece obtained by thefollowing process was used. The welded metal cut out from the thickstructural member was embedded in a resin, and a baffed finish wasapplied to the embedded welded metal. Electrolytic etching is thenapplied to this resulting metal using 10 percent oxalic acid as anetching solution, thereby yielding the microstructure. The test piece inwhich the microstructure has been yielded by the above-mentioned processwas used. The structure photograph that has been taken is shown in FIG.5 which will be described later in detail.

In the test of welding performance, presence or absence of scalegeneration on the bead surface of the welded metal on the thickstructural member (SS400) shown in FIGS. 2A and 2B was visually checked.

The effect of this embodiment will be specifically described, based oneach test result shown in Table 3. In each of Comparative Examples 1, 3,8, 9, and 11, the content of Ta is less than 1 mass % that is the lowerlimit, and in Comparative Example 10 the content of Mo is also less than1 mass % that is the lower limit. Thus, the tensile strength of each ofComparative Examples 1, 3, 8, 9, 10 and 11 at 350° C. was less than 485MPa. In Comparative Example 2, the content of Ta exceeds 10 mass %, andthe content of Mo exceeds 6 mass % that is the upper limit. Thus, thetensile strength of Comparative Example 2 at the room temperatureexceeded 800 Mpa. On contrast therewith, the contents of Ta and Mo ineach of Examples 1 to 16 meet composition requirements of the presentinvention. Thus, a good characteristic of tensile strength that exceeded610 MPa at the room temperature and exceeded 485 Mpa at 350° C. wasobtained. Specifically, a good tensile strength was obtained in therange of the content of Ta: 1 to 10 mass % and in the range of thecontent of Mo: 1 to 6 mass %, as shown in Tables 2 and 3.

FIG. 3 graphically shows dye penetrant test results of many weldingmaterials of Ni-based alloy 690 including Examples of the presentinvention and Comparative Examples, by sensitivity analysis using aneural network. FIG. 3A shows a relationship between Nb and the numberof cracks, while FIG. 3B shows a relationship between Ta and the numberof cracks. The number of cracks indicates the number of defects detectedby the dye penetrant test. Referring to FIGS. 3A and 3B, the number ofcracks on the build-up surface increases with an increase in the contentof Nb, as shown in FIG. 3A. On contrast therewith, even if the contentof Ta is increased, the number of cracks does not increase, as shown inFIG. 3B. This tendency shown in FIGS. 3A and 3B agrees with the factthat, although a defect has occurred in Comparative Example 3 (havingthe condition that the content of Nb exceeds 0.5 mass % and the contentof Ta is less than 1 mass %), no defect has occurred in each of Examples1 to 16 (having the condition that the content of Nb is 0.5 mass % orless and the content of Ta is 1 to 10 mass %).

The content of S in each of Comparative Examples 6 to 8 exceeds 0.0015mass % (15 ppm) that is the upper limit. In each of Comparative Examples6 to 8, consequently, the number of cracks exceeds 10 pieces, and thetotal length of the cracks in each of Comparative Examples 6 to 8exceeds 7 mm in the side bend test. Thus, Comparative Examples 6 to 8 donot satisfy the technical standards for welding (defined in theministerial ordinance No. 81). On contrast therewith, under thecondition of the content of S: 0.0015 mass % or less as shown inExamples 1 to 16, good weld cracking resistance was obtained.

FIG. 4 is a graph where the dye penetrant test results of the lot ofwelding materials of the Ni-based alloy 690 including Examples of thepresent invention and Comparative Examples are outlined, by thesensitivity analysis using the neural network. This FIG. 4 shows arelationship between the content of S in each welding wire formed by theTIG welding and cracks detected by the side bend test. Referring to FIG.4, it has been found that the number of cracks tends to transitionallyincrease when the content of S is in the range of 0.001 mass % (10 ppm)to 0.002 mass % (20 ppm). Thus, preferably, the content of S is set tobe 15 ppm or less.

The content of Al is less than 0.01 mass %, and the content of Ti isless than 0.01 mass % in Comparative Example 4. Thus, the content of Aland the content of Ti do not satisfy the composition requirements of thepresent invention. Consequently, a remarkable cracking has occurred inthe side bend test of the welded portion of the thick structural member,which does not satisfy the technical standards for welding (defined inthe ministerial ordinance No. 81). In Comparative Example 5, the contentof Al exceeds 0.7 mass %, and the content of Ti exceeds 0.7 mass %, andthe content of Al and the content of Ti do not satisfy the compositionrequirements of the present invention. Thus, a scale was generated onthe weld bead surface, as shown in Table 3. On contrast therewith, ineach of Examples 1 to 16, the content of Al is in the range of 0.1 to0.7%, and the content of Ti is in the range of 0.1 to 0.7%, and there isno scale generation on the weld bead surface (with good weldingperformance). Further, good weld cracking resistance was obtained.

The content of H exceeds 0.0015 mass % (15 ppm) in each of ComparativeExamples 8 and 10, and does not therefore satisfy the compositionrequirement of the present invention. Thus, a microvoid as shown in FIG.5B is generated, thereby impairing the integrity of the microstructure.On contrast therewith, the content of H is 0.0015 mass % (15 ppm) orless in each of Examples 1 to 16. Thus, it has been confirmed that theintegrity of the microstructure of the welded metal is maintained, asshown in FIG. 5A. H is mixed into the welding wire when the welding wireis drawn as well as when the welding wire is melted. That is, when alubricant is attached to the welding wire at the time of drawing thewelding wire, the content of H remarkably increases. Thus, the lubricantmust be fully washed away after the welding wire has been drawn.Comparative Example 12 is a welding wire that satisfies the conditionsdescribed in Patent Document 6 which is the related art. However, thecontent of Nb in Comparative Example 12 is high, and does not thereforesatisfy the composition requirement of the present invention. Thus, aweld cracking was generated in the dye penetrant test of the build-upwelded portion of the groove surface of the thick-walled plate, as shownin FIGS. 6A and 6B.

Though Ca+Mg as the inevitable impurity is not added to each of Examples1 to 16 in Table 2, the content of Ca+Mg is reduced to be less than0.002 mass % (20 ppm) in each of Examples 2 and 4 and Examples 9 to 12.When such an alloy composition is employed, scale generation on the beadsurface may be remarkably inhibited, in addition to improvement in thetensile strength and weld cracking resistance of the welded portion andimprovement in the integrity of the microstructure of the welded metal.The content of Ca+Mg in each of Comparative Examples 9, 10, and 12exceeds 0.002 mass % (20 ppm), and does not therefore satisfy thecomposition requirement of the present invention. Consequently, a scalewas generated on the build-up surface (weld bead surface) of multiplelayers, as shown in FIG. 6A. Analysis of the chemical composition ofthis scale has shown that this scale is an oxide mainly comprising Mg,as shown in FIG. 6B. On contrast therewith, no scale was generated onthe build-up surface of multiple layers in each of Examples 1 to 16.That is, in order to inhibit scale generation on the bead surface,preferably, Ca+Mg is not added, as in Examples 1 to 16, and the contentof Ca+Mg is reduced to be less than 0.002 mass % (20 ppm).

An alloy composition where the content of Cu is 0.08 mass % or less, andthe content of Co is 0.05 mass % or less is employed in each of Examples1 to 16, as shown in Table 2. Assume that such an alloy composition isemployed, and build-up welding is performed on the carbon steel plate.Then, weld cracking susceptibility does not increase due to reduction ofthe content of Cu, even if the dilution ratio has increased and aconsiderable amount of Fe is included in the build-up welded metal.Further, due to reduction of the content of Co, a radioactivity level ina working environment may be reduced when a periodic inspection or thelike is carried out. On contrast therewith, the content of Cu in each ofComparative Examples 1 and 10 exceeds 0.08 mass %. Thus, when build-upwelding is performed on the carbon steel plate and then the dilutionratio increases, weld cracking susceptibility cannot be reduced. Thecontent of Co exceeds 0.05 mass % in Comparative Example 6. Thus, aradioactivity level in the working environment cannot be reduced whenthe periodic inspection or the like is carried out.

As shown in Table 2, each of Examples 3 to 7 has an alloy compositionfurther including at least one kind of elements of B, Zr, and rare-earthelements (REM) of 0.02 mass % (200 ppm) or less in the alloy compositionin each of Examples 1 and 2 and Examples 8 to 16 described above. Withsuch an alloy composition is employed, an effect of further increasingthe weld cracking resistance at the welded port ion of the thickstructural member may be obtained. On contrast therewith, each ofComparative Examples 1 to 8 and Comparative Example 11 does not includeat least one kind of elements of B, Zr, and the rare-earth elements(does not include any of B, Zr, and the rare-earth elements). Thus, theeffect of further increasing the weld cracking resistance like that ineach of the examples 3 to 7 cannot be obtained.

When the high Cr Ni-based alloy welding wire in each of Examples 1 to 16as described above is employed, the tensile strength and the weldcracking resistance of the welded portion, the integrity of themicrostructure of the welded metal, and the welding performance(inhibition of scale generation) may be increased.

Next, an embodiment of a high Cr Ni-based shielded metal arc welding rodof the present invention will be described. Table 4 shows alloycompositions of welding wires used for high Cr Ni-based shielded metalarc welding rods of the present invention and alloy compositions ofComparative Examples for confirming an effect of the present invention.

TABLE 4 Chemical Compositions of Wires for Shielded Metal Arch WeldingRods (Mass %) Wire C Mn Fe P S Si Cu Ni Al Ti Cr Symbol (%) (%) (%)(ppm) (ppm) (%) (%) (%) (%) (%) (%) Comparative S1 0.008 5.21 8.27 50 100.06 0.02 Rem. 0.56 0.65 27.5 Example 13 Comparative S2 0.008 5.25 7.7660 7 0.12 0.01 Rem. 0.52 0.40 27.6 Example 14 Comparative S3 0.011 3.557.65 60 5 0.05 0.02 Rem. 1.22 0.45 27.7 Example 15 Comparative S4 0.0121.30 8.84 60 6 0.05 0.04 Rem. 0.65 1.31 29.6 Example 16 Example 6 Y60.016 0.35 8.58 110 4 0.32 0.02 Rem. 0.32 0.41 29.5 Example 10 Y10 0.0210.45 8.43 30 6 0.15 0.02 Rem. 0.26 0.37 29.5 Example 11 Y11 0.032 0.388.41 40 4 0.26 0.01 Rem. 0.28 0.40 29.8 Example 13 Y13 0.022 0.93 9.8450 10 0.26 0.03 Rem. 0.41 0.49 30.2 Example 14 Y14 0.029 1.12 6.54 60 100.32 0.02 Rem. 0.56 0.64 30.6 Example 15 Y15 0.016 1.22 7.42 80 12 0.280.01 Rem. 0.68 0.65 29.1 Example 17 S5 0.010 5.34 5.41 50 5 0.05 0.02Rem. 0.52 0.82 29.1 Example 18 S6 0.011 2.11 2.13 60 6 0.06 0.03 Rem.0.31 0.75 29.7 Example 19 S7 0.010 5.36 2.34 50 7 0.05 0.01 Rem. 0.290.97 27.5 Example 20 S8 0.012 1.22 2.66 70 10 0.04 0.04 Rem. 0.95 0.3830.2 Example 21 S9 0.010 5.22 1.11 50 4 0.03 0.01 Rem. 0.72 0.40 27.5Example 22 S10 0.012 3.06 5.32 30 8 0.06 0.02 Rem. 0.71 0.73 28.3 Nb TaMo Co O N H Ca + M B Zr REM (%) (%) (%) (%) (ppm) (%) (ppm) (ppm) (ppm)(ppm) (ppm) Comparative 3.11 0.50 0.31 0.01 20 0.009 7 — — — — Example13 Comparative 0.10 3.57 0.35 0.03 6 0.013 8 10 — — — Example 14Comparative 0.35 0.55 1.11 0.01 10 0.017 9 — — — — Example 15Comparative 1.75 2.58 5.88 0.04 13 0.014 7 — — — — Example 16 Example 60.01 2.33 4.20 0.03 50 0.005 13 — 10 50 60 Example 10 0.41 2.21 2.110.01 90 0.018 10 19 — — — Example 11 0.32 2.94 3.23 0.02 70 0.026 7 17 —— — Example 13 0.09 1.15 2.45 0.03 20 0.025 7 — — — — Example 14 0.072.84 3.43 0.005 25 0.008 11 — — — — Example 15 0.01 2.29 3.42 0.03 150.033 7 — — — — Example 17 1.50 2.51 1.77 0.02 20 0.011 7 10 — — —Example 18 1.72 0.01 2.51 0.01 10 0.018 10 — — — — Example 19 2.55 0.104.13 0.01 9 0.015 8 — — — — Example 20 0.51 2.45 3.64 0.02 12 0.017 7 —— — — Example 21 0.87 2.97 5.96 0.01 12 0.012 6 10 — — — Example 22 1.702.94 4.55 0.02 12 0.011 8 — — — —

Referring to Table 4, each of Examples 6, 10, 11, 13 to 15, and 17 to 22shows an example of the welding wire used for the high Cr Ni-basedshielded metal arc welding rod of the present invention. Referring toTable 4, Examples 6, 10, 11, and 13 to 15 are obtained by selecting apart of the high Cr Ni-based welding wires of various alloy compositionsshown in Table 2, as the wires for the shielded metal arc welding rods.Each of the examples shown in Table 4 has a composition comprising, bymass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si: 0.75% or less,Al: 0.26 to 1.0%, Ti: 0.36 to 1.0%, Cr: 25.0 to 31.5%, Nb: 3.0% or less,Ta: 3.0% or less, and Mo: 1 to 6%, and as inevitable impurities, P:0.02% or less, O: 0.01% or less, N: 0.1% or less, S: 0.0015% or less, H:0.0015% or less, Cu: 0.08% or less, and Co: 0.05% or less, and thebalance: Ni. By selecting a welding work condition whereby weld crackingsusceptibility is reduced, the welding wire of the present invention mayalso be used for the TIG welding.

Table 5 shows results of welding performance tests of the shielded metalarc welding rods produced with the welding wires for the high CrNi-based alloy welding rods of various alloy compositions shown in Table4. In the welding performance tests, each item of stability of an arc,spatter generation, slag encapsulation, slag detachability, slagburning, bead shape, and comprehensive evaluation of these items wereevaluated with one of marks of ∘ (good), Δ (passable), and X (bad).

TABLE 5 Wires Used for Shielded Metal Arc Welding Rods and Result ofWelding Performance Test* Wire Flux Arc Spatter Slag Slag Slag BeadComprehensive Symbol Type Stability Generation EncapsulationDetachability Burning Shape Evaluation Comparative S1 Lime ◯ ◯ ◯ ◯ X ◯ XExample 13-1 Comparative S2 Lime ◯ ◯ ◯ ◯ X ◯ X Example 14-1 ComparativeS3 Lime ◯ ◯ ◯ X Δ ◯ X Example 15-1 Comparative S4 Lime ◯ ◯ ◯ X Δ ◯ XExample 16-1 Example Y6 Lime ◯ ◯ ◯ ◯ ◯ ◯ ◯ 6-1 Example Y10 Lime ◯ ◯ ◯ ◯◯ ◯ ◯ 10-1 Example Y11 Lime ◯ ◯ ◯ ◯ ◯ ◯ ◯ 11-1 Example Y13 Lime ◯ ◯ ◯ ◯◯ ◯ ◯ 13-1 Example Y14 Lime ◯ ◯ ◯ ◯ ◯ ◯ ◯ 14-1 Example Y15 Lime ◯ ◯ ◯ ◯◯ ◯ ◯ 15-1 Example S5 Lime ◯ ◯ ◯ ◯ ◯ ◯ ◯ 17-1 Example S6 Lime ◯ ◯ ◯ ◯ ◯◯ ◯ 18-1 Example S7 Lime ◯ ◯ ◯ ◯ ◯ ◯ ◯ 19-1 Example S8 Lime ◯ ◯ ◯ ◯ ◯ ◯◯ 20-1 Example S9 Lime ◯ ◯ ◯ ◯ ◯ ◯ ◯ 21-1 Example S10 Lime ◯ ◯ ◯ ◯ ◯ ◯ ◯22-1 *Note: ◯ Good Δ Passable X Bad

Each of Examples 6-1, 10-1, 11-1, 13-1 to 15-1, and 17-1 to 22-1 inTable 5 shows a result of the welding performance test of the shieldedmetal arc welding rod produced with the welding wire in this embodimentfor the high Cr Ni-based alloy welding rod in Table 4 described above.

The high Cr Ni-based alloy shielded metal arc welding rods in Examples6-1, 10-1, 11-1, and 13-1 to 15-1 were respectively produced with thewires in Examples 6, 10, 11, and 13 to 15 in Table 4. The high CrNi-based alloy shielded metal arc welding rods in Examples 17-1 to 22-1were respectively produced with the wires in Examples 17 to 22 in Table4. As shown in Tables 4 and 5, a lime-type flux was used in each ofthese examples (Examples 6-1, 10-1, 11-1, 13-1 to 15-1, 17-1 to 22-1),for the reason that will be described later in detail.

The content of Nb in the wire in Comparative Example 13-1 exceeds 3.0mass %, and does not therefore satisfy the composition requirement ofthe present invention. The content of Ta in the wire in ComparativeExample 14-1 exceeds 3.0 mass %, and does not therefore satisfy thecomposition requirement of the present invention. Consequently, in thewelding performance test for each of the shielded metal arc welding rods(in Comparative Examples 13-1 and 14-1) using the wires of ComparativeExamples 13 and 14, slag burned on the bead surface of a welded portion.This burning may cause a defect in welding and may make it difficult toperform good welding, thus reducing welding performance. The content ofAl in the wire of Comparative Example 15-1 exceeds 1.0 mass %, and doesnot therefore satisfy the composition requirement of the presentinvention. The content of Ti in the wire of Comparative Example 16-1exceeds 1.0 mass 1, and does not therefore satisfy the compositionrequirement of the present invention. Consequently, in the weldingperformance test for each of the shielded metal arc welding rods (inComparative Examples 15-1 and 16-1) using the welding wires ofComparative Examples 15 and 16, slag detachability was bad, thus posinga great problem for efficiently performing a welding work. Slag alsoburned a little bit (which was evaluated with the mark of Δ). Oncontrast therewith, Examples 6-1, 10-1, 11-1, 13-1 to 15-1, and 17-1 to22-1 respectively show the shielded metal arc welding rods using thewires (of Examples 6, 10, 11, 13 to 15, and 17 to 22) that satisfy thecomposition requirements of the present invention and whose weldingperformances were good (were evaluated with the marks of ∘).

Table 6 shows alloy compositions of weld metals of the examples formedby the high Cr Ni-based alloy shielded metal arc welding rods producedwith the welding wires of the various alloy compositions and alloycompositions of Comparative Examples for confirming the effect of thepresent invention.

TABLE 6 Combinations of Wires and Flux Types Used for Shielded Metal ArcWelding Rods and Chemical Compositions of Weld Metals (Mass %) Wire FluxC Mn Fe P S Si Cu Ni Al Ti Cr Symbol Type (%) (%) (%) (ppm) (ppm) (%)(%) (%) (%) (%) (%) Comparative S1 Lime 0.030 4.32 8.32 60 15 0.27 <0.01Rem. 0.13 0.12 28.09 Example 13-1 Comparative S2 Lime 0.031 4.33 7.68 6020 0.30 0.01 Rem. 0.11 0.11 28.27 Example 14-1 Comparative S3 Lime 0.0323.81 9.10 60 20 0.22 0.02 Rem. 0.35 0.25 28.41 Example 15-1 ComparativeS3 Lime- 0.019 3.21 9.10 60 60 0.41 0.05 Rem. 0.20 0.02 28.21 ExampleTitania 15-2 Comparative S4 Lime- 0.021 4.28 8.84 60 20 0.45 0.04 Rem.0.06 0.03 29.86 Example Titania 16-2 Comparative Y22 Lime- 0.034 2.328.50 50 60 0.26 0.09 Rem. 0.08 0.15 29.65 Example Titania 17-2 Example6-1 Y6 Lime 0.031 2.10 8.34 80 10 0.25 0.03 Rem. 0.20 0.13 29.30 ExampleY10 Lime 0.034 0.81 8.14 50 45 0.15 0.02 Rem. 0.08 0.08 29.80 10-1Example Y11 Lime 0.039 0.69 8.25 40 10 0.25 0.02 Rem. 0.09 0.08 29.2211-1 Example Y13 Lime 0.031 0.91 8.81 40 10 0.25 0.02 Rem. 0.08 0.0829.27 13-1 Example Y14 Lime 0.034 1.81 7.22 70 10 0.26 0.02 Rem. 0.100.11 29.13 14-1 Example Y15 Lime 0.030 2.65 5.03 50 20 0.24 0.02 Rem.0.13 0.12 30.25 15-1 Example S5 Lime 0.030 4.45 6.13 40 15 0.11 0.03Rem. 0.10 0.15 29.18 17-1 Example S5 Lime 0.031 4.32 6.22 50 15 0.130.04 Rem. 0.14 0.16 29.45 17-2 Example S10 Lime 0.032 3.12 5.95 30 100.14 0.01 Rem. 0.14 0.16 28.77 22-1 Nb Ta Mo Co O N H Ca + Mg B Zr REM(%) (%) (%) (%) (%) (%) (ppm) (ppm) (ppm) (ppm) (ppm) Comparative 2.770.40 0.58 0.02 0.07 0.020 10 — — — — Example 13-1 Comparative 0.37 2.870.55 <0.01 0.06 0.018 12 — — — — Example 14-1 Comparative 0.21 0.48 1.21<0.01 0.07 0.022 15 — — — — Example 15-1 Comparative 0.15 0.33 1.09 0.040.07 0.020 22 — — — — Example 15-2 Comparative 2.54 4.45 6.31 0.04 0.070.018 25 — — — — Example 16-2 Comparative 0.75 2.17 3.87 0.06 0.07 0.01823 — — — — Example 17-2 Example 6-1 0.56 3.51 4.20 0.01 0.07 0.035 15 —20 20 10 Example 1.11 3.30 5.63 0.01 0.07 0.015 12 — 20 — — 10-1 Example0.15 2.61 2.93 0.02 0.08 0.033 15 10 — — — 11-1 Example 0.03 1.80 3.920.02 0.08 0.033 15 — — — — 13-1 Example 0.75 2.04 3.12 0.03 0.07 0.03315 — — — — 14-1 Example 0.95 3.30 2.77 0.03 0.07 0.025 10 — — — — 15-1Example 1.71 1.93 1.36 0.02 0.07 0.021 15 10 — — — 17-1 Example 1.222.21 3.51 0.01 0.07 0.034 10 — — — — 17-2 Example 1.33 0.52 4.03 0.010.07 0.02 10 — — — — 22-1

Examples 6-1, 10-1, 11-1, 13-1 to 15-1, 17-1, 17-2, and 22-1 in Table 6show the alloy compositions of the weld metals of high Cr Ni-basedalloys formed by shielded metal arc welding in this embodiment. The highCr Ni-based alloy weld metals formed by the shielded metal arc weldingin Examples 6-1, 10-1, 11-1, 13-1 to 15-1, 17-1, 17-2, and 22-1 wereformed by the shielded metal arc welding rods produced with the wires(in Examples 6, 10, 11, 13 to 15, 17, and 22) selected from among thewelding wires for the high Cr Ni-based shielded metal arc welding rodsin Table 4 described above. The weld metals in the examples shown inFIG. 6 each comprises, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1to 12%, Si: 0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0to 31.5%, Nb+Ta: 1.8 to 4.5%, Mo: 1 to 6%, and as inevitable impurities,Ca+Mg: less than 0.002%, P: 0.02% or less, S: 0.005% or less, H: 0.002%or less, N: 0.1% or less, O: 0.1% or less, Cu: 0.08% or less, and Co:0.05% or less, and the balance: Ni.

Table 7 shows evaluation results obtained after execution of tests ofwelding performances of the high Cr Ni-based alloy shielded metal arcwelding rods of various alloy compositions shown in Table 6, tensiletests of the weld metals, side bend tests of welded metal portions ofthick structural members, and check tests of microstructures of weldedmetals.

TABLE 7 Evaluation of Characteristics of Shielded Metal Arc Welding RodsTensile Strength (MPa) Test Presence of Comprehensive Temperature Resultof Side Bend Test on Welded Portion Absence of Evaluation of (° C.) ofThick Structural Member Microvoid in Welding Room Total Cracking WeldedMetal Performance* Temp. 350 Length (mm) No. of Defects Pass/Fail**Structure Comparative Example 13-1 X 612 484 7.8 11 Fail NoneComparative Example 14-1 X 600 481 6.5 9 Pass None Comparative Example15-1 X 577 466 6.5 7 Pass None Comparative Example 15-2 X 575 465 17.120 Fail Present Comparative Example 16-2 X 808 580 21.3 24 Fail PresentComparative Example 17-2 ◯ 728 558 18.9 23 Fail Present Example 6-1 ◯731 565 3.3 5 Pass None Example 10-1 ◯ 755 578 6.9 10 Pass None Example11-1 ◯ 702 551 1.0 2 Pass None Example 13-1 ◯ 646 516 1.8 3 Pass NoneExample 14-1 ◯ 715 554 2.2 4 Pass None Example 15-1 ◯ 741 566 4.2 5 PassNone Example 17-1 ◯ 718 559 4.3 5 Pass None Example 17-2 ◯ 729 560 4.9 7Pass None Example 22-1 ◯ 633 510 3.2 5 Pass None *Note: ◯ Good ΔPassable X Bad **Notes (Ministerial Ordinance No. 81): (1) A crackshould not exceed 3 mm in length (except those occurring at edge cornersof a test piece). (2) The total length of cracks having a length of 3 mmor less should not exceed 7 mm. (3) The number of cracks and/orblowholes should not exceed 10.

The welding wires (in Comparative Examples 13, 14, 15, and 16 shown inTable 4) used for producing the welding rods in Comparative Examples13-1 to 15-1 and Comparative Examples 15-2 and 16-2 do not satisfy thecomposition requirements of the present invention. Thus, there is aproblem of degradation of the welding performances of ComparativeExamples 13-1 to 15-1 and Comparative Examples 15-2 and 16-2 (see Table5).

The content of Nb+Ta in the weld metal in each of Comparative Examples15-1 and 15-2 is low, and does not therefore satisfy the compositionrequirement of the present invention. The content of Mo in each ofComparative Examples 13-1 and 14-1 is low, and does not thereforesatisfy the composition requirement of the present invention.Consequently, tensile strength at 350° C. in each of ComparativeExamples 13-1, 14-1, 15-1, and 15-2 was less than 485 MPa. That is, ascompared with Examples 6-1, 10-1, 11-1, 13-1 to 15-1, 17-1, 17-2, and22-1 that compositely include Nb+Ta and Mo, a satisfactory tensilecharacteristic cannot obtained from Comparative Examples 13-1, 14-1,15-1, and 15-2.

The content of Nb+Ta in Comparative Example 16-2 exceeds 4.5 mass %, anddoes not therefore satisfy the composition requirement of the presentinvention. For that reason, the total length of cracks exceeded 7 mm andthe number of the cracks exceeded 10 pieces in the side bend test of thewelded metal portion of the thick structural member in ComparativeExample 16-2. Thus, preferably, the weld metal in Comparative Example16-2 includes Nb to of 1.8 to 4.5 mass % or less and Mo of 1 to 6 mass%, as in each of Examples 6-1, 10-1, 11-1, 13-1 to 15-1, 17-1, 17-2, and22-1.

The content of S in each of Comparative Examples 15-2 and 17-2 exceeds0.005 mass % (50 ppm), and does not therefore satisfy the compositionrequirement of the present invention. For that reason, the total lengthof cracks exceeded 7 mm and the number of cracks exceeded 10 pieces inthe side bend test of the welded metal portion of the thick structuralmember. The total length of cracks and the number of cracks do notsatisfy the technical standards for welding (defined in the ministerialordinance No. 81). On contrast therewith, each of Examples 6-1, 10-1,11-1, 13-1 to 15-1, 17-1, 17-2, and 22-1 whose content of S is 0.005mass % or less (50 ppm) satisfies the technical standards for welding(defined in the ministerial ordinance No. 81). Thus, preferably, thecontent of S in the weld metal formed by using the shielded metal arcwelding rod of the present invention is set to 0.005 mass % (50 ppm) orless as in Examples 6-1, 10-1, 11-1, 13-1 to 15-1, 17-1, 17-2, and 22-1.

As described above, the influence of a flux and presence of Mn need tobe taken into consideration in the case of shielded metal arc welding.For that reason, the content of S in the weld metal (in each of Examples6-1, 10-1, 11-1, 13-1 to 15-1, 17-1, 17-2, and 22-1) formed by using theshielded metal arc welding rod in this embodiment is 0.005 mass % (50ppm) or less, while the content of S in each of the welding wires (inExamples 1 to 16 and Examples 17 to 22) described above is 0.0015 mass %(15 ppm) or less. Accordingly, the content of S acts on the total lengthof cracks generated in the side bend test for the welded portion of thethick structural member differently from the action shown in FIG. 4indicating the case of the TIC welding.

The content of H in each of Comparative Examples 15-2, 16-2, and 17-2exceeds 0.002 mass 1 (20 ppm), and does not therefore satisfy thecomposition requirement of the present invention. Thus, a microvoid wasgenerated in the welded metal. In addition, the number of cracksexceeded 10 pieces in the side bend test of the welded metal portion ofthe thick structural member in each of Comparative Examples 15-2, 16-2,and 17-2, and does not therefore satisfy the technical standards forwelding (defined in the ministerial ordinance No. 81). As describedabove, moisture absorbed by the flux in the shielded metal arc weldinggenerates hydrogen. Thus, the content of H in a welded metal formed bythe shielded metal arc welding tends to be higher than that formed bythe TIG welding. Generally, as flux types for a high Cr Ni-based alloyshielded metal arc welding rod, a lime-titania type mainly comprisingTiO₂, CaCO₃, and CaF₂ and a lime-type mainly comprising CaCO₃ and CaF₂are present. Out of these flux types, the lime-type flux was used forthe shielded metal arc welding rod of the present invention. The reasonfor the use of the lime-type flux is that the partial pressure of Hdecreases due to a gas component such as CO₂ to be generated from CaCO₃at a time of welding, so that the content of H in the welded metaldecreases more than with the other flux type. The CaF₂ component of theflux is melted into a molten slag during the welding, and then reactswith a molten metal, thereby controlling an increase of S and the like.Thus, the use of the lime-type flux is also effective for increasingweld cracking resistance.

The lime-titania type flux was used in Comparative Examples 15-2, 16-2,and 17-2. The content of H in each of Comparative Examples 15-2, 16-2,and 17-2 using such a lime-titania type flux exceeds 0.002 mass % (20ppm), as described above. Thus, the microvoid was generated in thewelded metal. For this reason, preferably, the lime-type flux is used,as in Examples 6-1, 10-1, 11-1, 13-1 to 15-1, 17-1, 17-2, and 22-1,thereby controlling the content of H to be 0.002 mass % or less.

The content of Cu in Comparative Example 17-2 exceeds 0.08 mass %. Thus,weld cracking susceptibility cannot be reduced when the dilution ratioincreases after build-up welding has been performed on a carbon steelplate. The content of Co in Comparative Example 17-2 exceeds 0.05 mass%. Thus, a radioactivity level in the working environment cannot bereduced when the periodic inspection or the like is carried out.

The welding performance of the high Cr Ni-based alloy shielded arcwelding rod having the alloy composition in each of Examples 6-1, 10-1,11-1, 13-1 to 15-1, 17-1, 17-2, and 22-1 is good. In the welded metalformed by each of these welding rods, tensile strength and weld crackingresistance of the welded portion and the integrity of the microstructureof the welded metal may be increased all together.

INDUSTRIAL APPLICABILITY

According to the present invention, the tensile strength characteristicand the weld cracking resistance of a welded portion and the integrityof the microstructure of a welded metal may be increased by configuringa high Cr Ni-based alloy welding wire to have an alloy compositioncomprising, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si:0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0 to 31.5%,Ta: 1 to Mo: 1 to 6%, and N: 0.1% or less, and as inevitable impurities,P: or less, O: 0.01% or less, S: 0.0015% or less, H: 0.0015% or less,Cu: 0.08% or less, and Co: 0.05% or less, and the balance: Ni, and byconfiguring such that the contents of S, Ta, Al, Ti, Mo, and N tosatisfy the following relations (1) and (2):

12000S+0.58Ta−2.6Al−2Ti≦19.3  (1)

Ta+1.6Mo+187N≧5.7  (2).

1. A high Cr Ni-based alloy welding wire comprising, by mass, C: 0.04%or less, Mn: 7% or less, Fe: 1 to 12%, Si: 0.75% or less, Al: 0.01 to0.7%, Ti: 0.01 to 0.7%, Cr: 25.0 to 31.5%, Ta: 1 to 10%, and Mo: 1 to6%, and as inevitable impurities, Ca+Mg: less than 0.002%, P: 0.02% N:0.1% or less, or less, O: 0.01% or less, S: 0.0015% or less, H: 0.0015%or less, Cu: 0.08% or less, and Co: 0.05% or less, and the balance: Ni,contents of S, Ta, Al, and Ti satisfying the following relation (1) andcontents of Ta, Mo, and N satisfying the following relation (2):12000S+0.58Ta−2.6Al−2Ti£19.3  (1)Ta+1.6Mo+187N³5.7  (2).
 2. A high Cr Ni-based alloy welding wirecomprising, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si:0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0 to 31.5%,Ta: 1 to 10%, and Mo: 1 to 6%, and as inevitable impurities, N: 0.1% orless, P: 0.02% or less, O: 0.01% or less, S: 0.0015% or less, H: 0.0015%or less, Cu: 0.08% or less, and Co: 0.05% or less, and the balance: Ni,contents of S, Ta, Al, Ti, Mo, and N satisfying the following relations(1) and (2):12000S+0.58Ta−2.6Al−2Ti£19.3  (1)Ta+1.6Mo+187N³5.7  (2).
 3. The high Cr Ni-based alloy welding wireaccording to claim 1 or 2, wherein the content of Al is 0.26 to 0.7 mass%.
 4. The high Cr Ni-based alloy welding wire according to any one ofclaims 1 to 3, wherein the content of Ti is 0.36 to 0.7 mass %.
 5. Thehigh Cr Ni-based alloy welding wire according to anyone of claims 2 to4, wherein the inevitable impurities further comprise: Ca and Mg; andthe total content of Ca and Mg is less than 0.002 mass %.
 6. The high CrNi-based alloy welding wire according to any one of claims 1 to 5,further comprising, by mass, Nb: 0.5% or less; the contents of S, Ta,Nb, Al, Ti, Mo, and N satisfying the following relations (3) and (4):12000S+0.58Ta+2.1Nb−2.6Al−2Ti£19.3  (3)Ta+3.8Nb+1.6Mo+187N³5.7  (4).
 7. The high Cr Ni-based alloy welding wireaccording to any one of claims 1 to 6, further comprising, by mass, atleast one kind of element selected from B, Zr, and rare earth elements:0.02% or less.
 8. A core wire for a shielded metal arc welding rodcomprising, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1 to 12%, Si:0.75% or less, Al: 0.26 to 1.0%, Ti: 0.36 to 1.0%, Cr: 25.0 to 31.5%,Nb: 3.0% or less, Ta: 3.0% or less, and Mo: 1 to 6%, and as inevitableimpurities, N: 0.1% or less, and, P: 0.02% or less, S: 0.0015% or less,O: 0.01% or less, H: 0.0015% or less, Cu: 0.08% or less, and Co: 0.05%or less, and the balance: Ni.
 9. A weld metal formed by shielded metalarc welding comprising, by mass, C: 0.04% or less, Mn: 7% or less, Fe: 1to 12%, Si: 0.75% or less, Al: 0.01 to 0.7%, Ti: 0.01 to 0.7%, Cr: 25.0to 31.5%, Nb+Ta: 1.8 to 4.5%, Mo: 1 to 6%, and as inevitable impurities,a total of content of Ca and Mg: less than 0.002%, N: 0.1% or less, P:0.02% or less, S: 0.005% or less, O: 0.1% or less, H: 0.002% or less,Cu: 0.08% or less, and Co: 0.05% or less, and the balance: Ni.
 10. Theweld metal formed by shielded metal arc welding according to claim 9,further comprising, by mass, at least one kind of element selected fromB, Zr, and rare earth elements: 0.02% or less.